* fixed memory leaks that occurred when liblinuxsampler was unloaded
* fixed a memory leak that could happen when a channel was deleted
while notes were playing
* fixed memory management bug in ASIO driver
* optimized the SynchronizedConfig class so it doesn't wait
unnecessarily long after an update

* code cleanup:
- global.h now only covers global definitions that are needed for the C++
API header files, all implementation internal global definitions are now
in global_private.h
- atomic.h is not exposed to the C++ API anymore (replaced the references
in SynchronizedConfig.h for this with local definitions)
- no need to include config.h anymore for using LS's API header files
- DB instruments classes are not exposed to the C++ API
- POSIX callback functions of Thread.h are hidden
- the (optional) gig Engine benchmark compiles again
- updated Doxyfile.in
- fixed warnings in API doc generation
* preparations for release 0.5.0

* fixed egoistic --instruments-db-location command line switch ;-)
which caused all subsequent command line switches to be ignored
* the default location of the instruments DB file can now be overridden
with ./configure --enable-default-instruments-db-location=/foo/bar.db
* instruments DB feature can be disabled at compile time with
./configure --disable-instruments-db (i.e. for cross compilation)
* in case instruments DB feature is disable at compile time, don't
actually compile the instruments DB source files and don't install the
instruments DB API header files either